The Organzation Codes for the NLECC are as follows:
ALPHA = ICE Investigators (Legacy Customs Agents). It only applies to Special Agents, not Detention and Removal Officers. They (DRO) are still using Legacy INS repeaters for the most part. They may come up on Sector NET's, but I've never heard them.
BRAVO= Headquarters. " Bravo 1" would be the Commissior of CBP
CHARLIE=Communictions. Charlie units are referred to as TCO's or Tactical Communications Officers. They work on all repeater site, conduct site acquistion, progamming, etc. They are also armed since they go to roofs and mountain tops in many remote and urban areas. "Charlie 100" is SECTOR communications in Orlando, FL. "100" signifies a Base.
DELTA=Port Headquarters
INDIA=CBP Officers (Legacy Customs Inspectors)
KILO=CBP K-9 Officers (Legacy Customs Canine Enforcement Officers)
LIMA=CBP Aviation Personnel
MIKE=CBP Marine Vessels
OMAHA=CBP Aviation Aircraft. "Hammer" is the AMO Headquarters in Riverside, CA. They are usually on HF, but do come up on VHF NET's every so often.
ROMEO=CMC (Customs Management Center)
SIERRA=used to be Legacy Customs OI Internal Affairs, but I believe ICE and CBP have separate OI's now, so I don't know.
TANGO=Task Force Officers
You will also hear several other users on the system like:
"Charlie Golf" = Coast Guard, FDA, ATF, etc. Some have call signs like ATF I heard is Whiskey (how appropriate), but I've only heard them say ATF.
Hope this helps.